mcs: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/mcs - from package: mono-core

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/mcs - from package: mono-mcs

You may install the required package with command apt-get install {package}

Error in other languages:
mcs: bevel nie gevind nie
mcs: comandă negăsită
mcs: comando não encontrado
mcs: commande introuvable
mcs: command not found
mcs: käsku ei ole
mcs: không tìm thấy lệnh
mcs: komanda nerasta
mcs: Kommando nicht gefunden.
mcs: kommandot finns inte
mcs: komut yok
mcs: nie znaleziono polecenia
mcs: níor aimsíodh an t-ordú
mcs: no se encontró la orden
mcs: no s'ha trobat l'ordre
mcs: opdracht niet gevonden
mcs: parancs nem található
mcs: perintah tidak ditemukan
mcs: príkaz nenájdený
mcs: příkaz nenalezen
mcs: команда не найдена
mcs: командата не е открита
mcs: 命令找不到
mcs: コマンドが見つかりません